1. Field of the Invention
The present invention relates to a semiconductor structure and the manufacturing method thereof, in particular, to a method for forming a semiconductor structure, and during the manufacturing process, performing the etching process for removing a work function layer only once.
2. Description of the Prior Art
Poly-silicon is conventionally used as a gate electrode in semiconductor devices, such as metal-oxide-semiconductors (MOS). With the trend towards scaling down the size of semiconductor devices, conventional poly-silicon gates face problems such as boron penetration and unavoidable depletion effect leading to inferior performance. Because of these problems, the equivalent thickness of the gate dielectric layer increases, reducing the gate capacitance, and lowering a driving force of the devices. Therefore, work function metals that are suitable for use as high dielectric constant (high-k) gate dielectric layers are employed to replace the conventional poly-silicon gates as control electrodes.
In a complementary metal-oxide semiconductor (CMOS) device, one of the dual work function metal gate structures is used in an NMOS device and the other one is used in a PMOS device. It is well known that compatibility and process controls for the dual metal gate structure is more complicated, while thickness and composition controls for materials used in dual metal gate structure methods are more precise.
Therefore, to improve the performance and the yield of the semiconductor devices, or to lower manufacturing costs and reduce the manufacturing time is an important research direction.